Solvent refining process



Patented June 2l', 1938 UNITED STATES PATENT oFFicEff ard H. Gross,Beacon, N. Y.,

assignors to The Texas Company, NewYork, N. Y., a corporation ofDelaware Application February 6, 1935, Serial No. 5,214

` 8 Claims. (Cl. 196-13) phases, the above mentioned `retained bodiesare This invention relates to 'the treatment of hydrocarbon oil, andparticularly to a method of. treating hydrocarbon'oil, such as mineraloil, with 'a selective solvent. l

The invention broadly contemplates a process for solvent reiiningmineral oil for `the production of lubricating oil of high viscosityindex, low pour test. and other desired properties and characteristics.

The invention. comprises extractively treating mineral lubricating oilstock with a selective solvent, such as furfural, for example, whereinthe oil is separated into an extract phase containing low viscosityindex constituents of the oil together with some constituents ofintermediate viscosity index, and a rafnate phase comprising highviscosity index constituents of the oil and retaining some of theextract phase. The two resulting phases are separated, cooled, andcentrifuged or settled, to separate all or a portion of the retainedmatter. The retainedl matter thus separated from each phase isadvantageously returned all or in part to the zone of extraction whereinit is brought into contact with fresh oil undergoing treatment. y

In the case of a w -bearing oil, the raiiinate phase, after removal ofthe retained material, is

dewaxed for the production of low pour testV lubricating oil.

The process of this invention ist-particularly Well adapted to thesolvent refining of mineral lubricating oil stock with a solvent ofthecharacter of furfural, and wherein lthe extractive treatment with theselective solvent is effected at temperatures of around 200 F., or inthe range from about 150 to 250 that the railinate phaseresulting fromextraction at such temperatures may retain an appreciable amount ofextract phase material. Similarly, the extract phase may contain asubstantial quantity of relatively parafdnic oil of intermediateviscosity temperature characteristics. At the higher temperaturesprevailing, during -such extractions, the rafllnate a substantial amountof.` the solvent. This retained solvent contains dissolved thereinjacertain amount ol .extract phase oil. Also, at such temperatures, theextract phase may comprise substantial amounts of oil of intermediatevis cosity index due to the increased solvent power of the solvent atelevated temperatures. It has been found that by separately removing theextract and rafhnate phases from the extracy and subjecting each phaseto cooling, centrifuging or settling the cooled tion zone, and either F.It has been found oil tends to retaine largely, if not completely,separated therefrom. In the ease of the raflinat'e phase, it isadvantageous to subject it to centrifuging to remove the retainedextract phase material, while in the case of the extract phase, it isusually sufficient to cool and subject it to settling or standing only,in order to separate the retained oil of intermediate character.

so returned. On the other hand, the oil of intermediate characterseparated from 'the extract phase alone may be returned to theextraction zone. The latter oil may thus be referred to as a cycle oil.It isthought that substantial benet results by returning .this cycle oilto the extraction zone where its presence tends to favorably iniiuencethe subsequent separation of fresh oil into phases respectively rich inparainic and nonparainic constituents of the oil.

In the case of` certain oils being. treated as, for example, heavyresidual fractions derived from mixed base crudes, it has been foundthat improved results Vare realized by centriiuging the raflinate phaseresulting from extractionl with furfural at high temperatures. These,oils contain certain constituents of an asphaltic nature which to someextent remain in the raffinate phase. It has'been found that thisasphaltic material can be readily removed by centrifuging the raffinatephase, even without prior cooling. The material removed by thecentrifuge is of a gelatinous nature and itsv removal results in aramnate oil of improved qualities as regards decreased carbon residue,resistance' to oxidation, stability of color, etc. as a consequence,subsequent acid treatment of the rafiinate oil, which would otherwise benecessar'y, may be avoided.

In order to more clearly describe the invention, reference will vnow bemade to th'accompanying drawing illustrating a flow diagram adapted tocarry out the process of our invention.

As shown in this drawing. the oil to be treated is drawn from a tank Iand introduced through aplpe 2 tothe lower portion-"of an extractor l.

. the incoming solvent and oil is such as to maintain-a suitabletemperature within the extractor as,for example, within the range fromabout 150 to about 250 F.

.The extractor 3 is of the tower type adapted to eil'ect countercurrentcontact between upwardly moving oil and downwardly moving solvent. In.order to bring about intimate contact between oil and solvent within theextractor, a suitable packing material, such as Raschig rings, may beprovided. On the other hand, mechanical agitating or stirring means maybe provided for bringing about the desired degree of contact followed bysuitable settling and decanting agitators and Asettlers may be arrangedso as to eiect countercurrent solvent action in a number of s uccessivestages.

As a result of this contact between oil and solvent, there results aformation of an extract phase containing the dissolved constituentsoftheoil, and a raiiinate phase comprising the undissolved paraiilnicconstituents of the oil. As previously mentioned,the extract phaseretains a portion of oil .of character intermediate as regards viscositytemperature relationship while the rainate phase retains a smallquantity of extract phase material.

The extract phase accumulates in the bottom of the extractor, while theramnate phase accumulatesin the upper portion thereof.

The raillnate phase is removed through a pipe 8 to a cooler 9 wherein itis cooled to a temperature ranging from about thirty to fty degreesbelow the extraction temperature. The amount: of cooling will dependupon the nature of the oil undergoing treatment. If the oil issubstantially wax-free, cooling may be carried to an even lowertemperature. On the other hand, in the case of wax-bearing oils, it isdesirable to maintain the raffinate phase at a temperature above that atwhichit would tend to solidify.

'111e cooled oil is then introduced to a centrifuge or settling chamberIl to eiIe'ct separation of the retained extract phase material andother impurities of an asphaltic nature. In some cases, the ramnatephase oil may be introduced directly to the centrifugeA or settlerwithout previous cooling. The separated material is conducted to a tankII. The centrifuged or settled ramnate phase is then conducted to a tankI2, and from there to a still Il for the removal of any remainingsolvent. This solvent removed as a vapor is conducted to a cooler andcondenser 20, to which reference is made later.

The solvent-free ramnate oil is then conducted to a tank Il for auchfurther treatment as may -be desired. In the case of a wax-bearing oil,it

may be delivered to a dewaxlhg plant. yOn the other hand. if it is awax-free oil, it may, for example, be finished up by clay contactfiltration.

The extract phase is removed from the bottom of the extractor I througha coolerv Il wherein it is cooled to a temperature substantially belowthe 'extraction temperature as, for example.

around thirtyor fty degrees below such temperature. 'The cooled extractphase is then delivered to a settling chamber' I6, wherein the retainedoil of intermediate character, insoluble in the solvent at the lowertemperature. separates therefrom. j

The separated oil is removed to a tank II. The remaining extract phaseis drawn off to a tank I8 and from there to a still I9. The solvent isrelmoved from the oil in the still I9 as a vapor.

This vapor is drawn oil, along with solvent vapor from the still Il, toa cooler 20 wherein it is cooled and condensed for re-use. The residualextract oil is drawn off from the stillv I 9 to a tank 2| for suchfurther disposition as may be desired.

The extract phase material separated from the raiilnate phase andaccumulating in tank Il, to'

gether with the separated or cycle oil accumulating in the tank I1, isdelivered by a pump 22 through a pipe 23 to an intermediate point of theextractor 3, wherein it .mingles with oil undergoing treatment. Ifdesired, this material may be mixed either with the charge or thefurfural prior to introduction to the extractor 3.

On the other hand, the separated liquid from tank II may be mixed withfresh furfural entering the extractor 3 or may be introduced thereto ata point where the furfural within the extractor has the sameconcentration of extract in solution. The cycle oil from tank II may bemixed with the fresh charge to the extractor.

By Way of illustration, the application of t-he invention may bedescribed with reference to the treatment of a steam-reducedcylinderstock derived from Pennsylvania crude by countercurrent extraction withfurfural at a temperature of around 230 to 250 F., using about fiveparts of solvent to one part of oil. I The tests on the reduced cylinderstock before treatment will be as follows:

Gravity A. P. I 25.1 Flash "F 560 Fire "F 640 Saybolt universalviscosity- At 130 F 955 At 210 F 162 Pour "F v v 35 Carbon residue,percent 3.0v

When extracted with furfural under the conditions above stated, the oiland solvent will'separate into a raiiinate phase comprising about 15.0%by volume, and an extract phase comprising about 85.0% by volume.

When the above ramnate and extract phases are separated and the solventremoved therefrom by distillation in the presence of steam, the tests onthe resulting railinate, oil and extract phase oil will be as follows:

If, instead of stripping outthe solvent from the raiilnate phase, asabove mentioned, it is cooled to about 180 1". and centrifuged at' thattemperatureaquantityotretainedextractphase material and some solventwillbey separated from the railinate'plnse. The separated extract phasematerial will amount to about 2.3% by volume of the raflinate phase andwill comprise a heavy black material, which after removal of the solventwill have a high carbon residue content of around 2.39%.

Similarly, if the extract phase, upon removal from the extraction zone,is cooled and settled at a temperature of about 150 F., oil otherwiseretained in the extract phase at the extraction temperature willvseparate from the mixture. This separated oil is of intermediatecharacter and will amount to about 6% of the original extract phase.

The centrifuged ranate phase, as well as the oil separated from theextract phase, retains a small amount of furfural which may be removedvby distillation. However, if theraffinate phase is to be dewaxed,v theretained solvent may remain therein throughout the dewaxing operation.Likewise, where the oil separated from the extract phase is beingreturnedtothe extraction zone, it will be unnecessary to remove theretained solvent prior to its return. f

The raffinate oil obtained by centrifuging the rafiinate phase and theoil separated by cooling the extract phase will, after stripping out anyremaining solvent, have the following tests:

Centri- Oil separated fuga from exrainate tract phase Gravity A. P. ize. 1 21. o 575 520 045 610 423 21s 169 94 l. 30 1. 52

It will be observed from the foregoing that centrifuging of theraffinate phase resulted in the removal of a substantial amount of heavymaterial, namely, 2.3% by volume and having a residual carbon content of2.39%; also,that by cooling and settling the extract phase, a relativelylarge amount of oil of intermediate character was separated. This`separated material, according to the process of our invention, isreturned to the extraction zone, all or in part, and mixed with freshoil undergoing treatment.

The remaining extract phase may be stored for such further dispositionas may be desired. The centrifuged raffinate oil, in the case of a.wax-bearing oil, is then mixed with asuitable dewaxing solvent mixture,such as a mixture of acetone and benzol, for example, and dewaxed in theusual manner.

The process of this invention is not necessarily restricted toextraction with a specific solvent such as furfural, for it iscontemplated that other selective solvents having the essentialselective action of furfural as between constituents of the oil ofdiffering viscosity indices may be employed. Thus, the process of thisinvention is particularly applicable where the solvents ,employed areused at temperatures considerably elevated above normal atmospherictemperature. The ramnate and extract phases obtained when extractingwith such solvents as nitrobenzene, aniline and crctonaldehyde may beadvantageously )zreated in accordance with the process of our invention.

Furthermore,A the process of this invention is not limited to thetreatment' of any particular type of hydrocarbon oil or petroleumfraction. It is adapted to the treatment of either distillate orresidual fractions of petroleum.v

annees Obviously, many modifications and variations A of theinvention',as hereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

-f We claim: l

l. In the rening, with a selective solvent, of a heavy lubricating oilstock containing residual carbon-forming bodies which form with thesolvent a. small amount of material of a gelatinous nature and which isdiiiicultly removable from the resulting raffinate, the methodcomprisingextracting the oil with a solvent comprising furfural at atemperature of around 200 F., forming an extract phase containing lowviscosity index constituents of the oil and a rafnate phase containinghigh viscosity index constituents and a substantial amount ofsaidgelatinous material, removing the raffinate phase, and centrifuging therailinate phase while at an elevated temperature not substantially belowthe extraction temperature to remove the gelatinous material containedtherein.

2. In the refining, with a selective solvent, of a heavy residuallubricating oil stock containing residual carbon-forming bodies whichform with the solvent a small amount of material of a gelatinous natureand which is diicultly removable `from the resulting raiinate, the`method comprising extracting the oil with a solvent comprising furfuralat a temperature of around 200 F., forming an extract phase containinglow viscosity index constituents of the oil and a ramnate phasecontaining highi viscosity index constituents and a substantial amountof said gelatinous material, removing the raffinate phase, andcentrifuging the removed raiinate phase in the presence of all itsretained solvent While at an elevated temperature of around 180--200" F.to

l remove the gelatinous material 'contained theretemperature and therebyseparating retained heavy extract material, reducing the temperature ofthe extract phase to separate therefrom oil of intermediate viscosityindex, and removing the oil of intermediate character ,so precipitated.l

4. The method of refining mineral lubricating oil comprising extractingthe oil with furfural at a temperature in the range 150 to 250 F.,forming an extract phase containing low viscosity index constituents ofthe oil dissolved in the oil comprising extracting the oil with furturalat?l a temperature in the range 150 to 250 F. in an extraction zone,forming an extract phase containing low viscosity index constituents ofthe oil dissolved in the bulk of the solvent and a railinate phasecomprising high viscosity index constituents of the oil mixed with asmall amount of heavyA extract, removing the two phases, centrifugingthe removed raiiinate phase at a temperature not substantially below theextraction temperature and thereby separating retained heavy extractmaterial, reducing the temperature of the extract phase substantiallybelow said extraction temperature to separate therefrom oil ofintermediate viscosity index, removing the oil oi intermediate characterso precipitated, and

returning separated oil of intermediate charac' ter to aforesaidextraction zone. y

6. The method of refining mineral lubricating oil comprising extractingthe, oil with an extraction solvent, forming an extract phaseVcontaining low viscosity index constituents of the oil dissolved in thebulk of the solvent' andI a ramnate phase comprising high viscosityindex constituents oi' the oil mixed with a small amount of retainedheavy extract oil dissolved in extraction solvent amounting to about 2%of the raiilnate phase and suspended in said raiinate phase. removingthe two phases, and without substantially altering .the solventcomposition. eentrifuging the removed raffinate phaseat a temperaturesubstantially the same as the extraction temperature and therebyseparating the small amount of retained heavy extract material. withoutseparation of the raiiinate into liquid phases.

7. The .method of reiining mineral lubricating oil comprising extractingthe'oil with an extraction solvent, forming an extract'phase containinglow viscosity index constituents of the oil dissolved in the bulk of thesolvent and a 10 raiilnate phase comprising high viscosity indexconstituents of the oil mixed with a small amount of retained heavyextract oil dissolved in extraction solvent, removing the two phases,centriiuging the removed raiiinate phaselat atem-` 15 perature of around180 to 200 F. and thereby separating retained heavy extract material,-reducing the temperature of the extract phase substantially below saidextraction temperature to separate therefrom oil of intermediateviscosity index, and removing the oil of intermediate character soprecipitated. v

8. 'I'he method of rening mineral lubricating oil by selective solventextraction comprising extracting the oil with a selective solvent,forming an extract phase containing low viscosity index constituents ofthe oil dissolved in the bulk of the solvent and a raiiinate phasecomprising high viscosity index constituents of the oil and containing asmallv amount of tarry materiall dissolved in solvent amounting toaround 2% or more of the' rafnate phase. removing the railinate phase,and centrifuging the removed raiiinate phase in the presence of all itsretained solvent and while at an elevated. temperatureof the order of150 F. and not substantially below the temperature at which the oil wasextracted with the selective solvent thereby to remove said small amountof tarry material without separation of the raiiinate into liquidphases. 40

RBERT E. MANLEY. BERNARD Y. MccARTY. HOWARD H. Gaoss.

